URANIUM CONTRIBUTIONS TO THE SAN JUAN RIVER FROM EPHEMERAL TRIBUTARIES

Uranium is a heavy metal with three isotopes, all of which are radioactive and have long half-lives. There are a variety of health concerns from inhalation and ingestion of uranium in addition to the concerns posed by its radioactivity. The southwestern United States has a history of uranium extraction and processing. The San Juan River is a major feature in the semi-arid Four Corners region of the Southwest as it is a vital source of water for drinking, irrigation, and recreation. The legacy of uranium mining and milling activity in the Four Corners region could contribute to high levels of uranium in these water systems. As part of a larger ongoing study observing the chemistry of ephemeral tributaries to the San Juan River, uranium contributions in these tributaries are being analyzed. The study area extends from Navajo Dam, NM, to Mexican Hat, UT. Scientists from the U.S. Geological Survey, Navajo Nation Environmental Protection Agency, and New Mexico State University are collecting samples from ephemeral tributaries as well as the San Juan River. From samples analyzed at the time of this abstract submission, out of the approximately 30 tributaries being analyzed in the study area, 12 have water samples with uranium concentrations greater than the 30 ug/L maximum contamination limit (MCL) set by the U.S. Environmental Protection Agency. During the Summer of 2021, water samples from Chaco River, a tributary that joins the San Juan River near Shiprock, NM, exceeded the MCL for uranium 7 times, and water samples from Marble Wash, a tributary that joins the San Juan River near Four Corners, exceeded the MCL for uranium 3 times. Three other tributaries, Red Wash, Gallegos Canyon, and Mancos Creek all have water samples with uranium concentrations that exceeded the 30 ug/L MCL twice. Contribution and sources of uranium to the San Juan River can be evaluated by focusing the analysis on tributaries that consistently have high uranium concentrations. This poster discusses progress to date and further work planned for this project.